Washing device for porous hollow fiber membranes, and porous hollow fiber membrane production method

Abstract

This invention relates to a washing device for a porous hollow fiber membrane, including: n (n is an integer of 2 or greater) washing tanks that contain a washing liquid, through which the porous hollow fiber membrane sequentially passes; and at least one pressure applying unit that pressurizes or de-pressurizes the washing liquid on the outer side of the porous hollow fiber membrane immersed in the washing liquid to force the washing liquid to pass through a membrane part of the porous hollow fiber membrane, in which the pressure applying unit is accommodated in at least one of the first to (n−1)-th washing tanks. According to the invention, it is possible to provide a porous hollow fiber membrane production method that is capable of reducing the concentration of residual substances in membrane retained water and preventing reattachment of a hydrophilic polymer.

1 . A washing device for a porous hollow fiber membrane, comprising:
 n (n is an integer of 2 or greater) washing tanks that comprise a washing liquid, through which the porous hollow fiber membrane sequentially passes; and   at least one pressure applying unit that pressurizes or de-pressurizes the washing liquid on the outer side of the porous hollow fiber membrane immersed in the washing liquid to force the washing liquid to pass through a membrane part of the porous hollow fiber membrane,   wherein the pressure applying unit is accommodated in at least one of the first to (n−1)-th washing tanks.   
     
     
         2 . The washing device for the porous hollow fiber membrane according to  claim 1 , wherein the pressure applying unit comprises:
 two or more de-pressurization washing units that de-pressurize the washing liquid on the outer side of the porous hollow fiber membrane immersed in the washing liquid to force the washing liquid to pass from the inner side of the porous hollow fiber membrane to the outer side thereof, and   at least one pressurization washing unit that pressurizes the washing liquid on the outer side of the porous hollow fiber membrane immersed in the washing liquid to supply the washing liquid to the inner side of the porous hollow fiber membrane from the outer side thereof,   wherein   the de-pressurization washing units and the pressurization washing unit are arranged in series, and wherein   the pressurization washing unit is accommodated in at least one of the first to (n−1)-th washing tanks.   
     
     
         3 . The washing device for the porous hollow fiber membrane according to  claim 1 , further comprising:
 supply means used to supply the washing liquid to at least one of the second to n-th washing tanks.   
     
     
         4 . The washing device for the porous hollow fiber membrane according to  claim 1 , wherein the pressurization washing unit is further accommodated in the n-th washing tank. 
     
     
         5 . The washing device for the porous hollow fiber membrane according to  claim 1 , wherein the de-pressurization washing units are disposed at opposite ends of an arrangement comprising the de-pressurization washing units and the pressurization washing unit. 
     
     
         6 . The washing device for the porous hollow fiber membrane according to  claim 2 , wherein a pressure range of the pressurization washing unit is 0.01 MPa or greater and smaller than 1 MPa. 
     
     
         7 . The washing device for the porous hollow fiber membrane according to  claim 2 , wherein a pressure range of the de-pressurization washing units is −0.1 MPa or greater and smaller than 0 MPa. 
     
     
         8 . A porous hollow fiber membrane production method, comprising:
 a coagulation process of coagulating a membrane forming dope that comprises a hydrophobic polymer and a hydrophilic polymer in a coagulating liquid to form a porous hollow fiber membrane; and   a hydrophilic polymer removal process of washing the porous hollow fiber membrane to remove the hydrophilic polymer that remains in the porous hollow fiber membrane,   wherein:   the hydrophilic polymer removal process comprises at least one pressure washing process of pressurizing or de-pressurizing, with respect to the porous hollow fiber membrane that sequentially passes through the insides of n (n is an integer of 2 or greater) washing tanks that comprise a washing liquid, the washing liquid on the outer side of the porous hollow fiber membrane to force the washing liquid to pass through a stem of the porous hollow fiber membrane, wherein the pressure washing process is performed m 1  (m 1  is an integer of 1 or greater) times in all, and wherein   the pressure washing process is performed for the porous hollow fiber membrane that passes through at least one of at least the first to (n−1)-th washing tanks.   
     
     
         9 . The porous hollow fiber membrane production method according to  claim 8 , wherein, with respect to the porous hollow fiber membrane that sequentially passes through the insides of the n (n is an integer of 2 or greater) washing tanks that comprise the washing liquid, the pressure washing process comprises:
 a de-pressurization washing process of de-pressurizing the washing liquid on the outer side of the porous hollow fiber membrane to force the washing liquid to pass from the inner side of the porous hollow fiber membrane to the outer side thereof, and   a pressurization washing process of pressurizing the washing liquid on the outer side of the porous hollow fiber membrane to supply the washing liquid to the inner side of the porous hollow fiber membrane from the outer side thereof,   wherein   the de-pressurization washing process and the pressurization washing process are performed m 2  (m 2  is an integer of 3 or greater) times in all, and wherein   the pressurization washing process is performed for the porous hollow fiber membrane that passes through at least one of at least the first to (n−1)-th washing tanks.   
     
     
         10 . The porous hollow fiber membrane production method according to  claim 8 , further comprising:
 supplying the washing liquid to at least one of the second to n-th washing tanks.   
     
     
         11 . The porous hollow fiber membrane production method according to  claim 8 , further comprising:
 performing the pressurization washing process for the porous hollow fiber membrane that passes through the n-th washing tank.   
     
     
         12 . The porous hollow fiber membrane production method according to  claim 8 , wherein at least the first and m 2 -th processes are the de-pressurization washing processes. 
     
     
         13 . The porous hollow fiber membrane production method according to  claim 8 , wherein the pressurization washing process comprises pressurizing in a pressure range that is 0.01 MPa or greater and smaller than 1 MPa. 
     
     
         14 . The porous hollow fiber membrane production method according to  claim 8 , wherein the de-pressurization washing process comprises de-pressurizing in a pressure range that is −0.1 MPa or greater and smaller than 0 MPa.